Safety wiring or lock wiring is a method used for preventing fasteners such as bolts from loosening in use. The practice of lock wiring involves the securing together of two or more parts of a fastener with a thin gauge metal wire, referred to as lock wire. The lock wire is secured to the bolts in such a way that the forces which would otherwise cause the parts to loosen act to further tighten the lock wire, thereby increasing the resistance to loosening. Lock wiring is commonly used for applications where a high degree of mechanical reliability of the fastening is important, such as in aircraft where the parts experience large vibration forces and a critical environment. Locking wiring also provides a mechanism of tamper proofing the fastenings, as the lock wire must be broken to allow the fastening to be loosened. The presence of the wire also provides a visual indication to the maintenance engineer that the bolt has been properly torqued, or if the wire is seen to be broken that tampering has occurred.
The application of lock wire must be performed properly by a skilled installation engineer in order to ensure the bolt or other threaded fastening is proper secured. Referring to FIG. 1, during wire locking a hole 2 must be drilled into the accessible part of the threaded fastener 1, which may be the head of the bolt 4, as shown in FIG. 1, or a nut. The fastener 1 is then secured in position and the correct fastening torque applied. Where the component includes more than one fastener, for example a threaded pipe coupling having two nuts, both of the nuts of the fasteners are drilled and secured. A length of lock wire 6 is then cut to length and as shown in FIG. 2 is then threaded through the holes 2 of the each of the fasteners 1, 8 in turn, with the wire 6 being twisted to apply a required tension and to secure the wire 6 in position between the fasteners 1,8. When this process is completed, the loose end of the wire are cut at a suitable length to ensure the ends of the wire are held together and do not unravel.